1. Field of the Invention
The invention relates to a display apparatus using a display panel comprising spontaneous light emitting devices such as organic electroluminescence devices or the like and relates to a driving circuit for the display apparatus.
2. Description of Related Art
An organic electroluminescence (hereinafter, abbreviated to xe2x80x9cELxe2x80x9d) device is known as a spontaneous light emitting element for realizing a thin display apparatus of a low electric power consumption.
FIG. 1 is a diagram schematically showing the structure of the EL element.
As shown in FIG. 1, the EL element is made in a manner that an organic functional layer 102 of at least one layer comprising an electron transport layer, a light emitting layer, a hole transport layer, and the like and a metal electrode 103 are laminated over a transparent substrate 100 made of a glass plate or the like on which a transparent electrode 101 has been formed.
FIG. 2 is an equivalent circuit diagram electrically showing characteristics of the EL element.
As shown in FIG. 2, the EL element can be represented by a capacitive component C and a component E of diode characteristics which is coupled in parallel with the capacitive component.
When a direct current is applied across the transparent electrode 101 and the metal electrode 103 by applying a plus voltage to an anode of the transparent electrode 101 and applying a minus voltage to a cathode of the metal electrode 103, charges are accumulated in the capacitive component C. When the applied voltage exceeds a barrier voltage or a light emission threshold voltage that is peculiar to the EL element, a current starts flowing from the electrode (on the anode side of the diode component E) into the organic functional layer serving as a light emitting layer, so that the organic functional layer 102 emits light at intensity which is proportional to the current.
FIG. 3 is a diagram schematically showing the structure of an EL display apparatus for displaying an image by using an EL display panel formed by arranging a plurality of EL elements in a matrix shape.
In FIG. 3, cathode lines (metal electrodes) B1 to Bn serving as the first to nth display lines and m anode lines (transparent electrodes) A1 to Am arranged so as to cross the cathode lines B1 to Bn are formed on an ELDP 10 as an EL display panel. EL elements E11 to Enm having the structure as mentioned above are formed at the cross points of the cathode lines B1 to Bn and anode lines A1 to Am, respectively. Each of the EL elements E11 to Enm corresponds to one pixel of an ELDP 10.
A light emission control circuit 1 converts supplied image data of one picture plane (n rows, m columns) into pixel data groups D11 to Dnm corresponding to the respective pixels of the ELDP 10, namely, the EL elements E11 to Enm and sequentially supplies those data every row to an anode line driving circuit 2 as shown in FIG. 4.
For example, the pixel data D11 to D1m correspond to m data bits for designating whether each of the EL elements E11 to E1m belonging to the first display line of the ELDP 10 is allowed to execute the light emission or not. When each data bit is at the logic level xe2x80x9c1xe2x80x9d, it indicates xe2x80x9clight emissionxe2x80x9d. When each data bit is at the logic level xe2x80x9c0xe2x80x9d, it indicates xe2x80x9cnon-light emissionxe2x80x9d.
The light emission control circuit 1 supplies a scanning line selection control signal for sequentially scanning each of the first to nth display lines of the ELDP 10 to a cathode line scanning circuit 3 synchronously with supplying timings of the pixel data of one row as shown in FIG. 4.
The anode line driving circuit 2 first extracts all of the data bits at the logic level xe2x80x9c1xe2x80x9d designating xe2x80x9clight emissionxe2x80x9d from the m data bits in the pixel data groups. The anode line driving circuit 2 subsequently selects all of the anode lines belonging to the xe2x80x9ccolumnxe2x80x9d corresponding to each of the extracted data bits from the anode lines A1 to Am, connects a constant current source only to the selected anode lines, and supplies a predetermined pixel drive current i.
The cathode line scanning circuit 3 alternatively selects the cathode line corresponding to the display line shown by the scanning line selection control signal from the cathode lines B1 to Bn, sets the selected cathode line to a ground potential, and applies a predetermined high potential Vcc to each of the other cathode lines. The high potential Vcc is set to almost the same value as that of the voltage across the EL element (voltage which is determined on the basis of a charge amount into the parasitic capacitor C) at the time when the EL element emits the light at a desired luminance.
The anode line driving circuit 2 allows the light-emission drive current to flow between the xe2x80x9ccolumnxe2x80x9d to which the constant current source is connected and the display line set to the ground potential by the cathode line scanning circuit 3. The EL element formed so as to cross the display line and the xe2x80x9ccolumnxe2x80x9d emits the light in accordance with the light-emission drive current. Since no current flows between the display line set to the high potential Vcc by the cathode line scanning circuit 3 and the xe2x80x9ccolumnxe2x80x9d to which the constant current source is connected, the EL element arranged to cross the display line and the xe2x80x9ccolumnxe2x80x9d is maintained in the xe2x80x9cnon-light emissionxe2x80x9d state.
When the operation as mentioned above is executed on the basis of the pixel data groups D11 to D1m, D21 to D2m, . . . , and Dn1 to Dnm, a light emission pattern of one field according to the supplied image data, namely, an image is displayed on the screen of the ELDP 10.
In recent years, to realize a large screen size of the display panel, it is necessary to increase the number of display lines, namely, the number of cathode lines B and increase the number of anode lines A, thereby realizing a highly fine screen. Since a circuit scale of each of the anode line driving circuit 2 and cathode line scanning circuit 3 also enlarges due to an increase in number of anode lines A and number of cathode lines B, therefore, there is a fear of deterioration of the yield in association with an increase in chip area when both of those circuits 2 and 3 are formed in one IC. To avoid it, there is an idea of constructing each of the anode line driving circuit 2 and cathode line scanning circuit 3 by a plurality of IC chips.
If the anode line driving circuit 2 is made of a plurality of IC chips, there however can be a case that the current amounts of light-emission drive currents to be supplied to the anode lines differ among the IC chips due to a variation occurred in the manufacturing process, or the like. Consequently, there is a problem that regions of difference luminance values are formed on the screen of the ELDP 10 due to the difference of the light-emission drive currents.
The invention has been made to solve the problems and it is an object of the invention to provide a display apparatus and a driving circuit of a display panel, in which even when an anode line driving circuit is made of a plurality of IC chips, light emission luminance values on the display panel can be uniformed.
According to the invention, there is provided a display apparatus comprising: a display panel made by forming a light emitting element as one pixel in each cross portion of a plurality of first electrode lines and a plurality of second electrode lines arranged so as to cross each of the first electrode lines; and a driving unit for performing light-emission driving of the display panel, wherein the driving unit is made of a plurality of driving circuits having a plurality of light-emission drive current sources each for generating a light-emission drive current to allow the light emitting device to emit the light and supplying the light-emission drive current to the first electrode line, and at least one of the plurality of driving circuits is provided with a drive current control circuit for adjusting a current amount of the light-emission drive current to be generated by the one driving circuit based on the light-emission drive current generated by the other driving circuit.
According to the invention, there is provided a driving circuit of a display panel, for performing light-emission driving of the display panel made by forming a light emitting device serving as one pixel in each cross portion of a plurality of first electrode lines and a plurality of second electrode lines arranged so as to cross each of the first electrode lines, wherein the driving circuit comprises: a light-emission drive current source for generating a light-emission drive current to allow the light emitting device to emit the light and supplying the light-emission drive current to a partial electrode group in each of the first electrode lines; a drive current control circuit for adjusting a current amount of the light-emission drive current on the basis of an input control current; and a control current output circuit for generating a control current of the same current amount as that of the light-emission drive current and supplying the control current.